Pressure operated device for a pressure operated servo-turbine

ABSTRACT

A pressure operated device for a pressure operated servo-turbine actuating a screw drive spindle or the like for driving a part of a machine tool. In the device the means of diverting a pressure medium jet, acting on reversible servo-turbine blades which can turn in opposite directions, can be adjusted by pressure medium pulses from a jet nozzle control device. The control vane of the latter can be set by means of a setting part which can be mechanically displaced or tilted, in accordance with setting or regulation deviations.

United States Patent [1 1 Moosmann Nov. 27, 1973 PRESSURE OPERATEDDEVICE FOR A PRESSURE OPERATED SERVO-TURBINE [76] inventor: AloisMoosmann, l1,

Muttergartenweg, Stuttgart-Birkach, Germany [22] Filed: Mar. 3, 1972[21] Appl. No.: 231,590

[52] 0.8. CI. 415/61 [51] Int. Cl. F0ld 1/24 [58] Field of Search 415/1,61

[56] References Cited UNITED STATES PATENTS Moosmann 415/61 PrimaryExaminer-C. J. Husar Attorney-Watson, Cole, Grindle & Watson [5 7ABSTRACT A pressure operated device for a pressure operatedservo-turbine actuating a screw drive spindle or the like for driving apart of a machine tool. In the device the means of diverting a pressuremedium jet, acting on reversible servo-turbine blades which can turn inopposite directions, can be adjusted by pressure medium pulses from ajet nozzle control device. The control vane of the latter can be set bymeans of a setting part which can be mechanically displaced or tilted,in accordance with setting or regulation deviations.

8 Claims, 7 Drawing Figures 1 PRESSURE OPERATED DEVICE FOR A PRESSUREOPERATED SERVO-TURBINE BACKGROUND OF INVENTION 1. Field to whichInvention Relates This invention relates to a pressure operated devicefor a pressure operated servo-turbine for the actuation of a screw drivespindle or the like for setting or regulating devices, such as, moreparticularly, a screw drive spindle for displacing. a slide or the likeof a machine tool.

2. The Prior Art The settingof tool or workpiece holding devices onpartly or completely automatically operating machine tools is carriedout using servo-motors of the most various different types in accordancewith the requirements to be met. These servo-motors are controlled byfeelers, which are moved along templates or masters for the purpose ofcopying, or by a numerical data input from an information storagedevice, which as a rule is a punched tape, via electrical means, such asan electromagnetically operated drive piston in the case ofhydrostatically operating servo-motors, such as pistons and cylinders,or radial or axial piston motors. It is also a known practice to dividethe desired slide travel into as many part-displacements or steps aspossible and to transmit the latter to an electrical stepping motor. Thestepping motor reacts very rapidly to each step signaled to it and thenumber of steps per unit time can be very high. On this basis controldevices are known in the case of which a stepping motor transmits itsrotary steps to a pressure piston, which drives the servomotor. Ascrew-threaded part forming part of the servo motor shaft. If thestepping motor turns to drive the piston, the latter is also movedaxially by the thread and so controls or drives the servo-motor in onedirection of rotation or the other until the screw-thread between thedrive piston and the servo-motor shaft has screwed back owing to itsmovement and has screwed the control piston back into the normal orneutral position.

Owing to the generally accepted limits of hydrostatic servo-systems asregards their sensitivity of response and therefore as regards theminimum deviation between intended and target values, the accuracy whichcan be achieved is limited even in the case of known systems of knownstepping motor drive piston hydraulic motor systems. Apart from theproblems which are caused by the hydrodynamic forces at the controledges of the drive piston, the lengths of the drive piston and the motorshaft give rise to problems of thermal sensitivity since they areinfluenced by the variations in the temperature of the hydraulic oil useand therefoFe undergo corresponding changes in length. Furthermore,every screw-thread engagement is subject to a certain degree of play, inthe case of the use of rolling elements with or without preloading,there is a certain elasticity. Added to this there are certainuncertainties due to limited stiffness of the motor shaft and the motorhousing which make themselves felt more especially when the direction ofmovement is reversed. All these difficulties can hardly be influenced toan appreciable extent by improving manufacturing accuracies.

SUMMARY OF INVENTION In order to increase the sensitivity of responseand the accuracy of the machine tools or the like a hydrodynamicservo-motor has been developed in accordance with the invention whichhas a very high sensitivity. In this system a feeler displacement of0.0002 mm suffices to reverse the direction of movement of the machineslide or carriage and a feeler displacement of 0.0004 mm is sufficientto bring about a reversal from full power operation in one direction tofull power operation in the other direction.

In the case of the extraordinarily high degree of elasticity for thisrange of accuracy with presently conventional machine tools it isconvenient to exclude the latter from the regulation circuit orloop,'more especially havingregard to the stabilisation of theservo-system. By using a correspondingly rigid construction of themachine tool itself and of its transmission parts the accuracy inherentin the control system can be transmitted to the workpiece to bemachined.

In connection with attaining the above-mentioned aim the presentinvention is based upon a servo-control device using a pressure operatedturbine, in the case of which the device for diverting a pressure mediumjet, acting on reversible servo-turbine plates which can turn inopposite directions, can be adjusted by pressure medium pulses from ajet nozzle control device, whose control vane can be set by means of asetting part, which can be mechanically displaced or tilted, inaccordance with the setting or regulation deviations.

, The invention resides essentially in that the target value datasupplied by a stepping motor and the actual value data device from theservo-turbine of the control device are compared with each other in avalue comparison device and the differences between the target andactual values are converted into movements of a cam part, whose cam facecan be sensed by a setting part of the control vane of the jet nozzlecontrol device.

Preferably a differential drive is used as a value comparison device,and it is supplied with the target value data of the stepping motor andthe actual value data of the servo-turbine from both sides via shaftsand its differential movements are transmitted to the cam part.

The cam part can be constructed in various different manners. Preferablyit consists of a rotary cam disc, driven for example by a spur gearwheel of the differential drive, with a control edge or the like,against which one end of a pin-shaped sensing or setting part lies whoseother end engages the control vane of the jet nozzle control device. Inorder to cut out thermal effects on the accuracy of the control deviceas far as possible the cam disc can be borne on a pin, for example,which is carried in rolling element bearings so as to be rotatable andaxially displaceable, and the end, carrying the cam disc, of the pin issupported by means of a pin on a fixed bearing, while the free end ofthis pin is supported by means of a further pin in an axially yieldingbearing body.

For the accuracy of the control device it is very important for theinvention that the bearing end face of the pin, which is arranged on theend, carrying the cam disc, of the pin of the cam disc, lie exactly inthe plane of the control face of the cam disc, so that the influence ofvariations in temperature at this position is practically deprived ofeffect.

LIST OF SEVERAL VIEWS OF DRAWING Further features of the invention aredescribed in more detail in the following description referring to adrawing.

FIG. 1 shows a longitudinal section through the pressure medium controldevice.

FIG. 2 shows a longitudinal section through the differential drive.

FIG. 3 shows a cross section through the differential drive.

FIG. 4 shows a view of the guide strip spring.

FIG. 5 shows a view of the control face of the cam disc.

FIG. 6 is a view of the control shoulder or offset portion.

FIG. 7 shows a section through the knife group of the control feelerwith displacement limiting means.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows the shaft stub l to bea shaft of the servo-turbine. The latter is connected via couplings 2and 3 with the differential sun wheel 4 of a shaft 5. These transmissionparts transmit actual value of the servomotor to be controlled to thedifferential transmission. The target value is passed by a steppingmotor 6 via a coupling 7, a shaft 8 and a sun wheel 9 to thedifferential transmission. The two planetary wheels 10 and 11 arejournalled on pins 12 and 13 in carriers 14 and 15, which are connectedtogether by means of a housing 16. The carrier 15 is provided with spurgear teeth 17, which mesh with teeth 18 of a cam disc 19. The front face20 of the latter is so made that its two surface havles lie in twoplanes offset by 0.001 mm in the axial direction. The two planes orhalves or one of them forms a control edge 38 (see FIG. 6).

The cam disc 19 is capable of being moved axially and rotated in onehousing half with its pin or shaft 21 and the two cylinder rollerbearings 22 and 23. The axial guidance of the cam disc is brought aboutin an adjustable manner by means of a screw 25. The latter is providedwith a thrust bearing 26 of sapphire, and against the bearing 26 therelies a tungsten carbide pin 27 of the cam disc so that the cam disc isheld firmly against the screw 25. On the opposite side there presses ascrew 28 acting via a thrust bearing 29 mounted axially resiliently inthe screw itself, which presses against a tungsten carbide pin 30 of thecam disc 19 so that the latter is held in abutment against the screw.This ensures that temperature changes in the longitudinal direction ofthe pin 21 do not have any effect on the control faces 20.

The control faces 20 are sensed by the sapphire needle 31 of apin-shaped setting part 32, which is guided in a friction-free manner bya strip spring 33. The pinshaped setting part 32 has a control vane 35which has an end 34 opposite to the sapphire needle 31 which acts on thecontrol vane 35 which consists of two oppositely placed knife edges 44and 45 and controls the air jet of a jet nozzle control device 36. Thecontrol vane 35 is under the action of a spring 37 urging it towards thepin-shaped setting part 32. The bearing face of the tungsten carbide pin27, which lies against the bearing face of the thrust bearing 26, mustbe so arranged that it lies exactly in the playing of the control face20 of the cam disc 19. This cuts out the influence of temperaturevariations on the feeling control device practically completely. In thecase of the pin-shaped setting part 32 a measure in this respect is notnecessary because this setting part lies in the flow of the spent air ofthe jet nozzle device and is thus held at a practically constanttemperature.

The control offset 38 with a height of 0.001 mm on the front face 20 ofthe cam disc 19 is so set by means of a screw 25 that on turning the camdisc 19 the pinshaped setting part 32 and thus the control vane 35 ispressed through a very small distance of approximately 0.0002 to 0.0003mm. This movement then brings about the rotation of the servo-turbine inthe one direction of rotation. If the cam disc 19 is turned in theopposite direction, the control disc 19 is removed from the sapphireneedle 31 so that the latter can move up against the half of the controlsurface 20 which is 0.001 mm lower. Owing to the action of the spring 37the pinshaped setting part 32 and the control vane 35 follow this smallmovement. The servo-turbine changes its direction of rotation andcontinues moving until the sapphire needle 31 comes to rest in themiddle of its displacement. This offset 38 of the front surface 20 of0.001 mm would appear to be the maximum which can be reached inmanufacture. On the other hand, however, only 0.0004 mm of displacementon the control vane 35 is required. For the actual construction thelimitation of the displacement of the vane 35 shown in FIG. 7 towardsthe front surface 20 is a simplification, since it makes the height ofthe offset 38 on the front surface 20 of the cam disc 19 devoid of anyimportance. A tungsten carbide bush 39 on the control vane 35, againstwhich the pin-shaped setting part 32 rests, is acted upon by the spring37 and abuts against the front face of a threaded sleeve, if it is notmoved clear of it by the pin-shaped setting part 32. The worm wheelcoupling between a screw head 41 and a worm gear 42 makes possible aparticularly sensitive or fine setting of threaded sleeve 40 inconjunction with a thread locking pin 43.

I claim:

1. In combination with a pressure operated servoturbine, especially formachine tools, having reversible servo-turbine plates capable of turningin opposite directions and adjustable by pressure medium pulses from ajet noule control device whose control vane is capable of being set bymeans of a setting part which can be mechanically displaced inaccordance with regulation deviations, a stepping motor, a valuecompanion device, said servo-turbine being operatively interconnectedwith said stepping motor through said value comparison device whichserves to compare the target value data supplied by said stepping motorwith the actual data derived from said servo-turbine, a pressure mediumoperated device comprising a rotatably mounted cam part operativelyinterconnected with said value comparison device, said cam part having acam face, said setting part of said control vane of said jet nozzlecontrol device being in contacting engagement with said cam face,whereby the differences between the target and the actual values areconverted into movements of said cam part.

2. The combination according to claim 1 wherein said value comparisondevice comprises a differential drive mechanism and a first drive shaftsupplying the target value data of said stepping motor thereto, andfurther comprises a second drive shaft supplying the actual value dataof said servo-turbine to said mechanism, whereby the deviations betweensaid stepping motor and said servo-turbine are transmitted to said campart.

3. The combination according to claim 1 wherein said cam part comprisesa rotary journalled cam disc, said differential drive mechanism having aspur gear wheel driving said cam disc, said face having surfaces offsetin an axial direction forming a control edge, said setting partcomprising an elongated pin, one end of said pin abutting against saidcontrol edge and the other end of said pin engaging said control vane ofsaid jet nozzle control device.

4. The combination according to claim 1 wherein said cam part comprisesa cam disc having an axial shaft journalled in roller element bearingsfor axial rotation, means comprising pin members at opposite axial endsof said cam part for permitting axial movement thereof, one of said pinmembers being journalled in a stationary bearing body and the other ofsaid pin members being supported in an axially yielding bearing body.

5. The combination according to claim 4 wherein screw means are providedfor adjusting each said bearing body.

6. The combination according to claim 3 wherein a strip spring isprovided for guiding said elongated pin in a friction-free manner whileabutting against said control edge.

7. The combination according to claim 1 wherein said control vanecomprises two oppositely disposed knife edges lying in a planeperpendicular to the jet direction of said jet nozzle control device,spring means in said control device urging said control vane against astationary abutment on said control device.

8. The combination according to claim 7 wherein said abutment comprisesan end face of an axially displaceable threaded sleeve.

1. In combination with a pressure operated servo-turbine, especially formachine tools, having reversible servo-turbine plates capable of turningin opposite directions and adjustable by pressure medium pulses from ajet nozzle control device whose control vane is capable of being set bymeans of a setting part which can be mechanically displaced inaccordance with regulation deviations, a stepping motor, a valuecompanion device, said servo-turbine being operatively interconnectedwith said stepping motor through said value comparison device whichserves to compare the target value data supplied by said stepping motorwith the actual data derived from said servo-turbine, a pressure mediumoperated device comprising a rotatably mounted cam part operativelyinterconnected with said value comparison device, said cam part having acam face, said setting part of said control vane of said jet nozzlecontrol device being in contacting engagement with said cam face,whereby the differences between the target and the actual values areconverted into movements of said cam part.
 2. The combination accordingto claim 1 wherein said value comparison device comprises a differentialdrive mechanism and a first drive shaft supplying the target value dataof said stepping motor thereto, and further comprises a second driveshaft supplying the actual value data of said servo-turbine to saidmechanism, whereby the deviations between said stepping motor and saidservo-turbine are transmitted to said cam part.
 3. The combinationaccording to claim 1 wherein said cam part comprises a rotary journalledcam disc, said differential drive mechanism having a spur gear wheeldriving said cam disc, said face having surfaces offset in an axialdirection forming a control edge, said setting part comprising anelongated pin, one end of said pin abutting against said control edgeand the other end of said pin engaging said control vane of said jetnozzle control device.
 4. The combination according to claim 1 whereinsaid cam part comprises a cam disc having an axial shaft journalled inroller element bearings for axial rotation, means comprising pin membersat opposite axial ends of said cam part for permitting axial movementthereof, one of said pin members being journalled in a stationarybearing body and the other of said pin members being supported in anaxially yielding bearing body.
 5. The combination according to claim 4wherein screw means are provided for adjusting each said bearing body.6. The combination according to claim 3 wherein a strip spring isprovided for guiding said elongated pin in a friction-free manner whileabutting against said control edge.
 7. The combination according toclaim 1 wherein said control vane comprises two oppositely disposedknife edges lying in a plane perpendicular to the jet direction of saidjet nozzle control device, spring means in said control device urgingsaid control vane against a stationary abutment on said control device.8. The combination according to claim 7 wherein said abutment comprisesan end face of an axially displaceable threaded sleeve.